Large monitors such as those used for maps generally include a plurality of adjacent rear projection screens which may typically have diagonal dimensions on the order of 72,84 or 100 inches. The screens are lenticular Fresnel lens screens and each screen typically has its own datagraphic projector.
If space is available, the projector may be mounted to project directly at the screen. If space is restricted the projector may be mounted above or below the screen and be directed at a mirror which in turn reflects the image on to the screen.
A typical projector, such as the Marquee.TM. 8000 projector manufactured by Electrohome Limited weighs on the order of 120 pounds. As each projector projects a portion of the overall image the projectors have to be supported and properly positioned behind the screen to ensure proper edge alignment of the adjacent images. The projectors should also be readily accessible for servicing and replacement.
Positioning of each projector requires that the projector be tiltable about various axes so that the image is movable horizontally, vertically and rotatably relative to the screen. Failure to properly position the projector will result in edge misalignment between adjacent images which, for example in the case of maps, will result in discontinuities of streets from one screen to another.
When the projectors are in use, heat is generated resulting in misalignment caused by thermal factors such as expansion. The projector mounting mechanism should be adjustable to compensate for such misalignment.
Previous inverted projector mounts for use in mirrored applications are inadequate for several reasons. Firstly, most prior projector mounts rely on relatively crude friction adjustment mechanisms which include slotted holes and locking nuts that can be slackened to enable movement between components and tightened to lock the components in place. Such adjusters do not enable very fine adjustment for precise alignment of adjacent images requiring that final adjustments be made by adjusting the electronic picture geometry circuits within the projector. Unfortunately an inherent trait of such projectors is that the decree of instability of the projected image increases so as to be proportionately more unstable as the degree of corrective adjustment is increased.
Also, most prior projector mounts require that a set-up technician move the projector's weight by hand against loosened friction adjusters. This not only limits the accuracy of the adjustment but also creates a safety hazard as the projectors may be 20 feet above the floor and only accessible by scaffolding or a ladder through an access opening.
The projector mounting and alignment device of the present invention, which is described in more detail below, enables a projector to be accurately positioned, adjusted within fine tolerances (on the order of .+-.0.5 pixel), further adjusted to compensate for image shifts which arise during projector use and also enhances access to the projector for projector replacement and servicing purposes.
A further feature of the present invention is that it provides for very fine adjustments to be made with minimal effort to enable a set-up technician to relatively safely align projected images without relying on the electronic picture adjustment circuits thereby maximizing image stability.
Yet another feature of the projector mounting and alignment device of the present invention is that the device enables the projector to be slid out of position for ease of access for servicing yet guides the projector back into its adjusted position without introducing any substantial amount of misalignment.